1. Technical Field
The present invention relates to a liquid ejecting apparatus on which a liquid ejecting head which ejects liquid through nozzle openings is mounted.
2. Related Art
With the development of a personal computer, a graphic processing can be executed relatively easily. Therefore, a liquid ejecting apparatus capable of outputting a hard copy of a color image, for example, which is displayed on a display, with high quality has been demanded. In order to meet such demand, there has been provided an ink jet recording apparatus on which an ink jet recording head which ejects ink droplets, for example, as liquid is mounted.
The ink jet recording apparatus gives noises of relatively small at the time of printing, and can form small dots at a high density. Therefore, the ink jet recording apparatus is used in various types of printing including color printing.
Such ink jet recording apparatus includes an ink jet recording head and a paper feeding unit. The ink jet recording head receives ink supply from an ink storage unit. The paper feeding unit moves a recording paper relatively with respect to the ink jet recording head. In the ink jet recording apparatus, ink droplets are discharged onto the recording paper from the ink jet recording head in accordance with a printing signal to form dots so that recording is performed.
Further, nozzle openings through which inks of black, yellow, cyan, and magenta can be discharged are provided on a common head holder (carriage). With this, not only text printing with the black ink but also full color printing can be performed by changing each discharge ratio of the inks.
Such ink jet recording head discharges ink pressurized in a pressure generation chamber as ink droplets onto a recording paper through the nozzle openings so as to perform printing. Therefore, there arises a problem that clogging is caused on the nozzle openings because of increase in ink viscosity due to the evaporation of a solvent from the nozzle openings, solidification of ink, adherence of dusts, mixing of air bubbles, or the like, resulting in printing failure.
In order to solve such problem, the ink jet recording apparatus includes a capping device and a cleaning device in many cases. The capping device seals peripheries of the nozzle openings of the ink jet recording head while printing is not performed. The cleaning device cleans a nozzle plate as needed.
The capping device not only has a function as a cap which prevents ink in the nozzle openings from being dried but also has a so-called cleaning function. To be more specific, the capping device also has the cleaning function of eliminating clogging of the nozzle openings by sealing the peripheries of the nozzle openings on the nozzle plate with a cap member and sucking ink from the nozzle openings with a negative pressure from a suction pump when the clogging occurs on the nozzle openings.
A discharge processing of forcibly discharging ink in order to eliminate clogging of the ink jet recording head is called a cleaning operation. Such cleaning operation is executed when printing is restarted after printing has not been performed for a long time or when a user presses a cleaning switch for eliminating clogging of the ink jet recording head. Further, the cleaning operation is a processing including a wiping operation by a cleaning member formed by an elastic plate such as a rubber after ink droplets have been discharged.
Further, the ink jet recording apparatus also includes a function of applying a driving signal, which does not relate to printing, to the ink jet recording head so as to make the ink jet recording head discharge ink droplets. This function is called a flushing operation. The flushing operation is executed every constant period for recovering an abnormal state of a meniscus in the vicinity of the nozzle openings of the head so as to prevent the clogging of the nozzle openings through which small ink droplets are discharged at the time of the printing from occurring (for example, see JP-A-2005-335404). The abnormal state of the meniscus in the vicinity of the nozzle openings is caused by the wiping operation or the like at the time of the cleaning operation.
In the configuration as described in JP-A-2005-335404, when a cap opening operation is performed, if liquid adheres to an abutment face of a cap member against a nozzle face (face on which the nozzle openings are formed) or the vicinity of the abutment face, a liquid film is formed on a space between the abutment face of the cap member against the nozzle face and the nozzle face when the cap member and the nozzle face are separated from each other. Note that the cap opening operation is an operation of separating the cap member from peripheries of the nozzle openings on a nozzle plate. The liquid film is formed when a capillary force acts on the space due to viscosity of the liquid droplets and the space has such a size that the capillary force acts thereon even if the abutment portion of the cap member against the nozzle face and the nozzle face do not abut against each other.
In a process where the cap member and the nozzle face are further separated from each other, the liquid film formed on the space is elongated. With this, a sealed space formed by the nozzle face and the cap member is enlarged so that a pressure in the sealed space is lowered.
If the pressure in the sealed space is lowered, the liquid film formed on the space is broken while being drawn to the inner side of the sealed space and scatters as splashing droplets. The pressure in the sealed space is a negative pressure immediately before the liquid film is broken. Therefore, almost all the splashing droplets fly toward the inner side of the sealed space. The splashing droplets fly while catching air present around the liquid film. Accordingly, fine air bubbles are contained in the splashing droplets.
As a result, if the splashing droplets reach to the nozzle openings, the fine air bubbles are drawn to a flow path from the nozzles with a negative pressure applied for maintaining shapes of the meniscuses on the nozzle openings. If the air bubbles are present in the liquid flow path, a pressure applied to a pressure generation chamber is reduced by the air bubbles before liquid is ejected. This causes ejection failure so that a problem arises.